Create WifiAnnotations and jarjar into framework

@IntDef annotations defined in the Wifi module are
@hide and cannot be referenced from the rest of
framework. Create a separate class for Wifi
annotations that can be jarjar'ed into external
clients.

Bug: 140299412
Test: compiles
Change-Id: I5beac976b4d12fb2c01f46cb46f9c54ab54618ea
diff --git a/wifi/Android.bp b/wifi/Android.bp
index e0b9ff3..26064cb 100644
--- a/wifi/Android.bp
+++ b/wifi/Android.bp
@@ -38,6 +38,11 @@
     ],
 }
 
+filegroup {
+    name: "framework-wifi-annotations",
+    srcs: ["java/android/net/wifi/WifiAnnotations.java"],
+}
+
 java_library {
     name: "framework-wifi",
     sdk_version: "core_platform", // TODO(b/140299412) should be core_current